Posterior tooth preparations /certified fixed orthodontic courses by Indian dental academy

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POSTERIOR TOOTH
PREPARATIONS
INDIAN DENTAL ACADEMY
Leader in continuing dental education


CONTENTS OF THE SEMINAR
Introduction of full veneer crowns
Rotary Instruments used for tooth preparation
Indications, contraindications, advantages, and
disadvantages.

Preparation for full veneer crowns
a. Complete cast metal crown
b. Posterior metal ceramic crown (wing prep.)
c. Cast ceramic crown




Introduction of partial veneer crowns



Rotary Instruments used for tooth preparation




Indications, contraindications, advantages, and
disadvantages
Preparation for partial veneer crowns
1)Three-quarter crown
2)Modified three-quarter crown
3)Seven-eighth crowns
4)proximal half crowns



Resin-bonded prosthesis


INTRODUCTION
Tooth preparation is a far more important
phase of fixed partial denture prosthesis
treatment although some practitioners never
realize this. It must be done with skill and
meticulous attention to detail, for everything
else that follows – pulpal vitality, periodontal
health, a good esthetic result, proper
occlusion, protection of remaining tooth
structure, and the longevity of the restoration
itself – will depend on it.

ROTARY INSTRUMENTS USED FOR
FULL VENEER PREPARATIONS
Shape
Round
end
diamond

Use
tapered 1.Depth orientation grooves
2.Occlusal reduction
3.Functional cusp bevel

Torpedo diamond
Short needle

Long needle

1.Axial reduction
2.Chamfer finish line
1.Initial interproximal axial
reduction in posterior teeth
1.Initial
proximal
axial
reduction in anterior teeth

Small wheel diamond
Tapered
(171L)

fissure

1. Lingual reduction in anterior
teeth
bur 1.Seating groove
2.Proximal groove (posterior
teeth
3.Smoothing and finishing
4.Occlusal and incisal bevels


Tapered fissure
(169L & 170L)

End cutting bur
Torpedo bur
Flame bur

burs 1.Initial groove alignment
2.Angles of proximal boxes
3.Smoothing and finishing
4.Occlusal and incisal bevels
Conventional shoulder finishing
1.Axial wall finishing
2.Chamfer finishing
1. Flare and bevel finishing


FULL VENEER CROWNS
COMPLETE CAST
CROWN

METAL CERAMIC

ALL CERAMIC CROWN


COMPLETE CAST METAL CROWNS
Complete cast metal crowns can be
used where the break down of tooth
structure is severe, to the extent that is
has been described in operative dentistry
as “the final attempt to preserve the
tooth”. The terms “full crown”, “full cast
crown” and “complete crown” can be
used interchangeably with full veneer
crown to describe a restoration entirely
made of cast metal.

Clinicians have long considered full veneer crowns
to be the most retentive of veneer preparations
Controlled laboratory studies have shown that
when compared with partial veneer designs, the
full veneer crown exhibits superior retention and
resistance
It does not mean that it must be used in every
case
Instead should be used on those teeth whose
restoration demands maximum retention.
Selection of full veneer retainer becomes
mandatory when the abutment tooth is small or
when the edentulous space is long.

Indications
Extensive destruction from caries or trauma.
Endodontically treated teeth.
Existing restoration that needs the use of a more
conservative restoration
Necessity for maximum retention and strength.
To provide contours to receive a removable appliance.
Other re-contouring of axial surfaces (minor corrections
of mal inclinations).
Correction of occlusal plane.
Contraindications
Should not be used in mouths with uncontrolled caries
Less than maximum retention necessary.
Esthetics.

Advantages
Strong.
High retentive qualities.
Usually easy to obtain adequate resistance
form.
Option to modify form and occlusion.
Contact areas can be conveniently developed.
Embrasure areas can be enhanced for
periodontally compromised dentition.
Disadvantages
Removal of large amount of tooth structure.
Adverse effects on tissue.
Vitality testing not readily feasible.
Display of metal.

TOOTH PREPARATION FOR COMPLETE CAST CROWN
Planar occlusal reduction is
done using round end tapered
diamond and no: 171 bur. Depth
orientation grooves are made on
the triangular ridges and primary
developmental
grooves.
The
depth orientation grooves should
be 1.5mm deep on functional
cusps and 1mm deep on nonfunctional cusps. The tooth
structures between the orientation
grooves are removed following
cuspal contours.

Functional cusp bevel is
done using round end
tapered diamond and no:
171 bur. Depth orientation
grooves are placed across
the facial occlusal line
angle of the mandibular
molar. The bevel should
parallel the inward facing
inclines of the cusps of the
opposing tooth, at a depth
of 1.5 mm usually forming
a 45 angle with the axial
wall.

Facial and lingual axial
reduction is done with a
torpedo
diamond
producing a definite
chamfer finish line at the
same time. The facial
and lingual reduction are
carried as far as possible
into the interproximal
embrasures
without
nicking the adjacent
teeth.

Mesial and distal axial
reduction. A short thin
tapered diamond is placed
against the facial surface
of
the
remaining
interproximal
tooth
structure. It is held upright
and
moved
up
and
down, directing it lingually
with light pressure. Once
sufficient space has been
produced, sweep the short
thin diamond back and
forth planing the surface to
smoothness.

Chamfer finishing.
Torpedo bur is used to
produce a distinct
finish line and to
round of the angles of
the preparation.


Seating groove is made
on the axial surface
using no: 171 bur. The
groove should be cut to
the full diameter and it
should extend gingivally
to a point 0.5 mm above
the chamfer.


Features of full veneer crown preparation and
the function served by each


METAL CERAMIC RESTORATION


The use of porcelain fused to metal
restorations has grown from the development
of the first commercially
successful
porcelain/ gold alloy restoration by Weinstein
et al in 1950’s. While a porcelain-fused to
metal crown can serve as a strong and
esthetic restorations, patients too often
receive this type of restoration for minor
irregularities that could have been better
handled by conservative treatment or none at
all.

Indications :
• Extensive tooth destruction – caries, trauma or
existing previous restorations
• The need for superior retention and strength
• An endodontically treated tooth in conjunction
with a suitable supporting structure (a post and
core)
• To recontour axial surface or correct minor
malinclinations
• Esthetics
• If all ceramic crown is contraindicated

Contraindications :
• Patients with active caries or untreated
periodontal disease
• Young patients with large pulp chambers
• When more conservative retainer is
technically feasible
• Intact buccal wall


Advantages :
• Superior esthetics as compared to
complete cast crown.
• Strength of cast metal is combined with
the esthetics of an all ceramic crown by
reinforcing a brittle, more cosmetically
pleasing material through support derived
from the stronger qualities are excellent.
• excellent retentive qualities

Disadvantages :
• Removal of substantial tooth structure.
• Subject to fracture because porcelain is
brittle.
• Difficult to obtain accurate occlusion in
glazed porcelain.
• Shade selection can be difficult.
• Inferior esthetics compared to all ceramic
crown.
• Expensive

POSTERIOR PORCELAIN FUSED TO
METAL CROWN PREPARATION


POSTERIOR PORCELAIN FUSED TO METAL
CROWN PREPARATION
Planar occlusal reduction
is done using round and
171 bur. Depth orientation
grooves are made on the
triangular
ridges
and
primary
developmental
grooves.
The
depth
orientation grooves should
be 1.5 to 2.0 mm in occlusal
areas
where
porcelain
coverage is required. The
tooth structures between the
orientation grooves are
removed following cuspal
contours.

Functional cusp bevel
is done using round end
171
bur.
Depth
placed across the lingual
incline of the maxillary
lingual cusp. The bevel
should parallel the inward
facing inclines of the
cusps of the opposing
tooth, at a depth of 1.5
mm usually forming a 45
angle with the axial wall.

Depth orientation grooves
A flat end tapered diamond is
first aligned with the occlusal
portion of the facial surface
and three vertical cuts are
made to the full diameter of
the diamond, fading out at the
“break” where the curvature of
the facial
surface is the
greatest. Two similar grooves
are made maintaining
the
same instrument parallel to
the gingival segment of the
facial surface. A single depth
orientation groove may also
be used.

Facial reduction, occlusal half: A flat end
tapered diamond is used to remove the
tooth structure remaining between the
orientation groove in the occlusal portion
of the facial surface.


Facial reduction, gingival
half: A flat end tapered
diamond is used to reduce
the gingival segment and
extend
well
into
the
proximal surface. 1.2 mm
to 1.4 mm is the accepted
reduction for a porcelain
fused to metal restoration.

Proximal axial reduction:
Short
needle
diamond
facilities
interproximal reduction with out nicking the
adjacent tooth. Once separation between
the teeth is achieved the needle diamond is
used to plane the proximal axial wall.


Lingual axial reduction: A torpedo
diamond is used for lingual axial
reduction and to round over the corner
created at the line angle with the
proximal surfaces.


Axial finishing: All axial
surfaces to be veneered with
metal are finished using a
torpedo
finishing
bur
producing the chamfer finish
line. The facial surface and
those areas of the proximal
surfaces to be veneered with
porcelain are smoothened with
the no: 171 bur. Lingual to the
proximal contact, the transition
from
the
deeper
facial
reduction to the relatively
shallower
lingual
axial
reduction result in a vertical
wall or “wing” of tooth
structure.

Shoulder finishing: No: 957 bur is
used to finish the shoulder and is
planed with a sharp 1.0 m wide chisel.

Gingival bevel: Flame diamond and
finishing bur are used to produce a
narrow bevel, no wider than 0.3 mm.


The features of a posterior porcelain fused to metal crown
and the function served by each.


CAST CERAMIC CROWN PREPARATION
Occlusal reduction: A
large round end tapered
diamond is used to place
depth orientation grooves
on triangular ridges and
major grooves. The final
occlusal reduction should
be 1.5 mm to 2.0 mm
deep. Remove the tooth
structure
remaining
between
the
depthorientation grooves with
the
large
round-end
tapered diamond. www.indiandentalacademy.com

Functional cusp bevel:
The large round end
tapered diamond is used
to
produce
depth
orientation grooves in
the facial incline of the
facial cusp. A minimum
of 1.5 mm of clearance is
necessary.


Facial and lingual axial
reduction: The large round
end tapered diamond is used
to obtain axial reduction
ranging from 1.0 to 1.5 mm
by making depth orientation
grooves and removing the
tooth
structure
between
them. The axial reductions
are carried out as far as
possible into the proximal
embrasures.

Complete axial reduction: A short needle
diamond is used to begin the proximal axial
reduction without touching the adjacent tooth.
The axial reduction interproximally is complete
by running the round end tapered diamond.


Preparation finishing: round end
tapered carbide bur is used to finish the
axial surfaces and the functional cusp
bevel.


The features of a cast ceramic crown preparation for
an all ceramic crown on a posterior tooth and the
function served by each.


PARTIAL COVERAGE CROWNS POSTERIORS


INTRODUCTION


• An extracoronal restoration that covers only
part of the clinical crown considered to be a
partial veneer crown. It can also be referred to
as a partial coverage restoration.


DEFINITION
• A restoration that restores all but one coronal
surface of a tooth, usually not covering the facial
surface.(GPT- 8)
• A partial veneer crown is a restoration covering two
or more surfaces of a tooth (Tylman)


TYPES OF PARTIAL COVERAGE
CROWNS
• For posterior teeth-1)Three-quarter crown
2)Modified three-quarter crown
3)Seven-eighth crowns
4)proximal half crowns


INDICATIONS FOR PARTIAL VENEER
CROWNS:
• Partial veneer crowns are a conservative measure and
are preferable to the complete veneer restoration.
• Intact or minimally restored teeth.
• Teeth with crown length that is average or that
exceeds the average.
• Teeth with normal anatomic crown form, i.e., without
excessive cervical constriction

CONTRAINDICATIONS FOR PARTIAL
VENEER CROWNS:

• High caries rate.
• Teeth with extensive restoration
• Deep cervical lesion – difficult to establish
finish line , if area is sensitive complete
coverage crown is indicated.


• Teeth with short clinical crown – difficult to
achieve resistance and retention form.
• Thin teeth – preparation of retention
grooves is difficult.
• Poor alignment of teeth in the dental arch.


ADVANTAGES OF PARTIAL VENEER
CROWNS:
Partial veneer crowns have several advantages over
complete crowns:
• The tooth reduction is conservative.
• The esthetics surpass the complete veneer cast
crown.
• Margin accessibility for finishing and cleaning is
improved.

• Complete seating of the casting is more
easily verified.
• Complete seating of the casting during
cementation is enhanced by diminished
hydraulic pressure.

• Electric pulp testing can be conveniently
accomplished on the intact enamel surface.

DISADVANTAGES OF PARTIAL
VENEER CROWNS:

• The partial veneer crown is not as retentive as
a complete veneer crown.
• Skillful preparation is critical to avoid metal
display.
• The partial veneer crown preparation is limited
to fairly intact teeth with normally shaped
crown and an www.indiandentalacademy.com clinical crowns
average length

Fundamental Principles of Design:
1) To impart strength to the remaining portion of
the tooth crown.
2) To provide maximum resistance and retention
form to the finished restoration.
3) To preserve esthetics by conservation of tooth
structure, thus limiting the display of gold on
buccal and labial surfaces.

ROTARY INSTRUMENTS USED FOR
TOOTH PREPARATIONS
•
•
•
•
•
•
•
•

Round end tapered diamond,
Torpedo diamond,
Short needle,
Long needle,
Flame diamond,
Small wheel diamond,
Tapered fissure burs
End cutting bur

Steps for preparation of partial veneer crowns
• Outline Form
• Lingual reduction
• Incisal reduction
• Lingual axial reduction
• Proximal axial reduction
• Proximal box or groove placement
• Occlusal or incisal offset placement

• Facial bevel
• Finishing the preparation.

Maxillary posterior three
quarter crowns


Occlusal reduction
• No. 171 or round-end
tapered diamond is
used
• Depth orientation
grooves are made on
the triangular ridges
and the developmental
grooves 1.0mm on the
non functional and
1.5mm on the
functional cusp

• At the occluso-facial
line angle groove is
made only 0.5mm deep
to minimize the
display of metal.

• Tooth structure from
between the grooves is
removed according to
cuspal contours

Functional Cusp Bevel
• Should be parallel to
the inward facing
inclines of the cusps
of the opposing tooth,
at depth of 1.5mm
creating 45˚ angle
with the axial wall.
• No. 171 bur

Lingual Axial Reduction
• Torpedo diamond
creating a definite
chamfer all over.
• Over inclination of
the lingual wall
frequently occurs.
• Check at all times
for over inclination.

Proximal Reduction

• Initially thin needle
diamond is used in
sawing motion to just
break the contact with
the adjacent tooth
• Once contact is
broken, torpedo
diamond is used to
create a definite
chamfer finish line
and complete the
axial and proximal
reduction.

Axial Finishing
• Torpedo bur is used to
finish the axial walls
and round of the
margins of the
preparation.


Proximal Groove

• Parallel to the incisal two
thirds of the facial surface.
• Orientation cut is made
using no.170 bur depth
1.0mm or less.
• Groove is continued
apically to about 0.5mm
above the chamfer finish
line.
• Grooves on mesial and
distal side are made parallel
to each other. www.indiandentalacademy.com

Proximal Flares
• Flame diamond and
flame bur is used to
produce the proximal
flares that is a flat
geometric plane.
• When access is good
a medium grit
sandpaper disc may
be used.

Occlusal Offset
• No. 171 bur used to
create a 1 mm ledge
on the lingual incline
of the facial cusp
connecting the
grooves and assuming
an inverted V shape.
No.957 end cutting
bur is used to define
the margins

Facial bevel
• Flame diamond is
used to bevel the
occluso-facial line
angle keeping it
perpendicular to path
of insertion. The
bevel should not be
more than 0.5mm
wide.

Completed three quarter crown


Features of the Maxillary Posterior
Three Quarter Crown Preparation


• A common variation of
the three quarter crown
preparation , employed
when caries or previous
restorations are present
on the proximal
surfaces, is one in which
boxes are substituted for
grooves.
• However boxes are very
destructive of tooth
structure, so their use
can be justified only
when tooth structure has
been destroyed by caries

• A less destructive
alternative for
augmenting retention
and resistance is a three
quarter crown
preparation utilizing two
grooves on each
proximal surface.
• There is no significant
difference between
retention afforded by the
four grooves and that
available from two
boxes.

Mandibular Posterior Three Quarter
Crown


Occlusal Reduction
• No. 171 or torpedo diamond is
used
• Depth orientation grooves are
made on the triangular ridges
and the developmental grooves
1.0mm on the non functional
and 1.5mm on the functional
cusp
• At the occluso-facial line angle
groove is made only 0.5mm
deep to minimize the display
of metal.
• Tooth structure from between
the grooves is removed
according to cuspal contours

Occlusal Shoulder
• No: 171 bur is used
to form the occlusal
shoulder along the
termination line of
the functional cusp
bevel facially. End
cutting bur is used
to plane the
shoulder (1.0 mm
wide).

Lingual Axial Reduction
• Torpedo diamond
creating a definite
chamfer all over.
Over inclination of
the lingual wall
frequently occurs.
• Check at all times
for over inclination

Proximal Reduction
• Initially thin needle
diamond is used in
sawing motion to just
break the contact with
the adjacent tooth
• Once contact is
broken, torpedo
diamond is used to
create a definite
chamfer finish line and
complete the axial and
proximal reduction

Axial Finishing
• Torpedo bur is
used to produce a
distinct finish line
and round of the
angles of the
preparation.


Proximal Groove

• Parallel to the incisal
two thirds of the facial
surface.
• Orientation cut is made
using no.170 bur depth
1.0mm or less.
• Groove is continued
apically to about
0.5mm above the
chamfer finish line.
• Grooves on mesial and
distal side are made
parallel to each other.


Proximal Flares

flame bur is used to
produce the facial
flares that is a flat
geometric plane.
When access is good
a medium grit
sandpaper disc may
be used.
• The flare is wider at
occlusal than at the
gingival with a definite
finish line.

Facial Bevel
no: 170 bur is used
to bevel the
occlusal shoulder.


Completed mandibular posterior three quarter
crown preparation

Proximal view

Occlusal view


Features of the Mandibular
Posterior Three Quarter Crowns


Reverse Three – Quarter
Crowns


• Complete coverage of
facial surface is used only
occasionally and is
usually reserved for one
or two situations
• It is ideal for restoration of
molars that are inclined
lingually.
• It can also be used on
molars that have suffered
destruction of the facial
surface, but not of the
lingual

Maxillary Posterior Seven Eighth
Crown


Occlusal reduction
• No. 171 or torpedo
diamond is used
• Depth orientation grooves
are made on the
triangular ridges and the
developmental grooves
1.0mm on the non
functional and 1.5mm on
the functional cusp
• At the occluso-facial line
angle groove is made
only 0.5mm deep to
minimize the display of
metal.
• Tooth structure from
between the grooves is
removed according to

• Done using round end
tapered diamond and
no: 171 bur. Depth
placed across the
lingual inclines of the
lingual cusps.
• The bevel should
parallel the inward
facing inclines of the
opposing tooth, at a
depth of 1.5 mm
usually forming a 45
angle with the axial

Facial and Lingual Axial
Reduction

• Is done with a torpedo
diamond producing a
definite chamfer finish
line at the same time.
• The lingual reduction
is carried as far as
possible into the
interproximal
embrasures with out
nicking the adjacent
teeth.
• The disto axial
reduction should end
1.0 mm mesial to

Proximal Axial Reduction
• A short thin tapered
diamond is placed
against the lingual
surface of the
remaining
interproximal tooth
structure and a sawing
motion is used.
Continue toward the
facial surface until
contact with adjacent
teeth is barely broken.
• Once sufficient space
has been produced, a
torpedo diamond is
used for axial
reduction and to

Grooves
to prepare a mesial
and a facial groove
correctly aligned
with the path of
insertion.


Flares
• A flame diamond
and carbide bur is
used to make the
mesial and facial
flares which are
narrow at the
gingival end and
wider occlusally.

Occlusal Offset
to produce a 1.0
mm wide ledge on
the lingual incline of
the facial cusp
connecting the
grooves, assuming
the shape of an
inverted V. Its floor
is perpendicular to
the path of insertion

Occlusal Finishing Bevel
• A flame diamond or
no: 170 bur is used
for creating an
occluso facial
finishing bevel. The
bevel is rounded up
to the proximal
occlusal line angle
to blend with the
proximal flares.

Completed seven eigth crown preparation


Features of the Seven-Eighth
Crown Preparation


Proximal Half Crowns


Occlusal Reduction

• Round end tapered
diamond and no: 171
bur.
• Depth orientation
grooves on the distal
aspect of the occlusal
surface 1.5mm deep.
Since the mesial
segment of the tooth is
dropped below the
occlusal plane the
grooves may not be as
deep.
• The tooth structures
between the orientation
grooves are removed
following cuspal www.indiandentalacademy.com
contours.

• Is done using round
end tapered diamond
and no: 171 bur.
Depth orientation
grooves are placed
across the facial
occlusal line angle of
the mandibular molar.
The bevel will be
shorter and shallower
on the mesial cusp
than on the distal.

Mesial Axial Reduction

• Torpedo diamond is
used for the axial
reduction by making the
path of insertion of
mesial surface parallel
with the long axis of the
premolar abutment.
• The end of the diamond
will eventually make
contact with the tooth in
the gingival area of the
mesial surface and
produce a chamfer finish
line.


Facial and Lingual Axial
Reduction
• Is done with a
tropedo diamond
producing a definite
chamfer finish line
at the same time.
End the extension
1.0 mm or more
mesial to the distofacial embrasure.

Occlusal Isthmus and
Countersink
• No: 171 bur is
used to make an
occlusal isthmus
and a countersink
in the distal fossa
to supplement
retention,
resistance and
structural
durability.

Facial and Lingual Grooves
• No: 171 bur is used to
make parallel grooves
on the facial and
lingual surfaces with in
1.0 mm of the vertical
distal extension of
preparation.
• The grooves should
be parallel to the
mesial surface of the
tooth and the long axis
of the other abutment.

Distal Occlusal Offset
• A V-shape offset
0.5 to 1.0 mm from
the distal occlusal
finish line
connecting the
lingual groove to
the countersink to
the facial groove is
made using no: 171
bur.

Flares and Occlusal Bevel
• A flame diamond is
used to place flares
distal to the facial
and lingual
grooves.
• A bevel is cut along
the distal marginal
ridge with the flame
diamond taking
care not to extend
into the distal
occlusal

Completed proximal half crown preparation


Features of the Proximal Half
Crown Preparation


REVIEW OF LITERATURE
• Anthony H.L Tjan et al (1979) have
discussed the functions of grooves and offset
of a three quarter crown and the types of
groove flare design possible. They have
established a practical guide to planing the
grooves on a three quarter crown which
fulfills biologic, mechanical & structural
requirements.

• Mitsuo Kishimoto et al (1983) studied
the retention and resistance of four
variations of three quarter crown
variations. Preparation with boxes or four
grooves were found to be the most
retentive of three quarter crowns used in
the study. Lingual placement of proximal
groove enhanced retention. Three quarter
crowns with V shaped groove had least
resistance. www.indiandentalacademy.com

• Potts RG, Shillingburg HT Jr,
Duncanson MG Jr. (1980). Five
preparation designs were tested for
retention and resistance.
• Retention values for all partial veneer
crowns were significantly lower than those
for the complete veneer crown.
• Resistance values increased significantly
with the addition of grooves and/or
extension of axial surface coverage.
• Addition of grooves and/or extension of
axial surface coverage produced small
increases in retention values but marked
increases in resistance values

RESIN BONDED FIXED
PARTIAL DENTURE


Definition
• Resin bonded prosthesis
A prosthesis that is luted to tooth
structure, primarily enamel, which has
been etched to provide mechanical
retention for the resin cement. -GPT-7


Indications
• Replacement of missing anterior teeth in
children and adolscents.
• Short span.
• Unrestored abutments.
• Single posteior tooth.
• Significant crown length.
• Excellent moisture control.

Contraindications
•
•
•
•
•
•

Parafunctional habits.
long edentulous spans.
Restored or damaged abutments.
Compromised enamel.
Deep vertical overlap.
Nickel allergy.


Advantages
•
•
•
•
•
•
•
•
•

Minimal removal of tooth structure
Minimal potential for pulpal trauma
Anaesthesia not usually required
Supragingival preparation
Easy impression making
Provisional not usually required
Reduced chair time
Reduced patient expense
Rebond possible.

Disadvantages
•
•
•
•

Reduced restoration longevity
Enamel modifications are required.
Space correction is difficult
Good alignment of abutment teeth is
required.
• Esthetics is compromised on posterior teeth.


Fabrication
• In the fabrication of resin-retained
FPDs, following three phases is necessary
for predictable success:
1. Preparation of the abutment teeth
2. Design of the restoration
3. Bonding


Preparation of the abutment teeth
• Common principles dictate tooth
preparation design.
– A distinct path of insertion must exist,
proximal undercuts must be removed to
provide "planes of metal" on the lingual and
proximal surfaces,
– occlusal rest seats and proximal groove slots
must provide resistance form, and a definite
and distinct gingival margin should be
established wherever possible.

• The tooth preparation includes
axial reduction and
guide planes on the proximal surfaces with a
slight extension onto the facial surface to
achieve a faciolingual lock.
should encompass at least 180 degrees of the
tooth to enhance the resistance
extended as far as possible to provide
maximum bonding area
should be a finish line which is placed about
1.0 mm supragingivally.

– Occlusal clearance is needed on very few teeth: 0.5 mm
is needed on maxillary incisors
– Vertical stops are placed on all the preparations
consisting of two or three flat countersinks on the lingual
surface of an incisor, a cingulum rest on a canine or an
occlusal rest seat on a premolar or molar .
– Wilkes found rests to be the dominant feature in a
preparation, contributing to both resistance and rigidity.
The occlusal rest directs the applied force from the
pontic to the abutments.
– Barrack strongly recommends the use of two rests.

– The resistance features used in a tooth preparation
for an acid etched resin-bonded retainer will normally
be grooves
– 31% to 77% in study by saad etal and 81% in study
by burgess et al found grooves were found to
increase resistance to displacement on anterior
preparations
– If there is an existing amalgam, all of the amalgam, or
at least all of its surface, is removed so that the box
form can be utilized
– BARRACK et al in his study proposed that the entire
occlusal outline of the existing amalgam restoration is
included within the outline of the retainer's occlusal
rest.
– HEMBREE et al in his study stated if the retainer
margins cross over an amalgam-enamel
margin, therewww.indiandentalacademy.com of leakage
is a high probability
occurring around that margin.

Preparation of posterior tooth
• The basic framework for the posterior
resin-retained FPD consists of three
major components:
– occlusal rest (for resistance to gingival
displace-ment),
– retentive surface (for resistance to occlusal
displacement), and
– proximal wrap and proximal slots (for
resistance to torquing forces)

• A spoon-shaped occlusal rest seat is placed in the
proximal marginal ridge area of the abutments adjacent
to the edentulous space. An additional rest seat may be
placed on the opposite side of the tooth .
• Proximal and lingual axial surfaces are reduced to
lower their height of contour to approximately 1 mm.
from the crest of the free gingiva.
• Proximal surfaces are prepared so that parallelism
results
• Occlusally, the framework should be extended high on
the cuspal slope, well beyond the actual area of enamel
recontouring
• A single path of insertion should exist. The alloy
framework should be designed to engage at least 180
degrees of tooth structure when viewed from the
occlusal .

• This proximal wrap enables the restoration to
resist lateral loading by engaging the
underlying tooth structure and is assisted in
this re-gard by grooves in the proximal just
lingual to the buccal line angle. Distal to the
edentulous space, the retainer resistance is
augmented by a groove at the lingual proximal
line angle.
• Moving a properly designed resin-bonded
FPD in any direction except parallel to its path
of insertion should,not be possible, nor should
it be possible to displace any tooth to the
buccal from the framework

• Preparation differs between maxillary and
mandibular molar teeth only on the
lingual sur-faces. The lingual wall of the
mandibular tooth may be prepared in a
single plane. The lingual surface of the
maxillary molars requires a two-plane
reduction due to occlusal function and the
taper of these functional cusps in the
occlusal two thirds.
• Lingually inclined mandibular molars
(this may require a two-plane
modification)

Preparation for
maxillary premolar

Preparation for
mandibular 2 premolar
Preparation for mandibular 1 premolar.
Placement of rest seat would leave very
little area in the lingual cusp of premolar
lingual cusp coverage when it does not
interfere in occlusion is an excellent means
of incerasing surface area and reinforcing
the retainer

• Preparation for
maxillary molar

• Preparation for
mandibular molar


Posterior resin bonded fixed partial denture
framework configurations.

• Standard
– 2 grooves one near the facioproximal angle
adjacent to the edentulous space and one at
the opposite linguoproximal corner, with 180
of axial wall convergence.


• Two rests : this variation suggested by barrack,
has axial coverage on both proximal walls and
the rest seats located near the central groove at
the mesio-occlusal and disto-occlusal. They resist
displacement by occlusal forces


Loops : these features are formed by
occlusal inlays being joined to a groove on
a lingual or proximal surface. They brace
the arms


• Lingual cusp coverage: lingual
cusps of mandibular molars
and premolars can be
covered to bolster the retainer
againist deformation.

Tilted molars: mesial and
particularly mesiolingual
tipped molars are out of
occlusion can be covered to
improve occlusion and
remove sublingual food
traps.


Other design concepts
• Occasionally, a combination restoration can be used. This
type of FPD includes a resin-bonded re-tainer on one of the
abutment teeth and a conven-tional cast restoration on the
other
• Periodontal splinting is the most demanding of the
restoration designs; splints and splint-FPD combinations
require care in designing adequate mechanical retention
• The posterior FPD splint uses multiple rests and distinct
mechanical retention of the abutment in the retainer, which
can be important when the abutment is the most distal
tooth in the arch
• The anterior splint must engage as much enamel as
possible to aid in retention and is more demanding in tooth
alignment and preparation design.

REFERENCES
•
•

•
•

Fundamentals of fixed prosthodonticsH.T.Shillingberg
Contemparary fixed prosthodonticsS.F.Roseintiel.
Tylman’s theory of practice of fixed
prosthodontics.
Fundamentals of tooth preparations H.T.Shillingberg, Jacobi, Brackett



Tjan AHL and Miller GD. Biometric guide to groove
placement on three quarter crown preparations. J Prosthet
Dent. 1979; 42: 405-410.



Kishimoto M, Shillingburg T, and Duncanson MG.
Influence of preparation features on retention and
resistance. Part II: Three quarter crown. J Prosthet Dent.
1983; 49: 188-192.



Potts RG, Shillingburg HT Jr, Duncanson MG Jr Retention
and resistance of preparations for cast restorations.J
Prosthet Dent. 1980 Mar; 43(3):303-8.


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